Speed sensor assembly

ABSTRACT

A robust and compact speed sensor assembly that includes a Hall effect sensor with protective circuitry in a compact housing that can be attached to the wheel of a motorcycle in the vicinity of the brake rotor to present the sensor Hall plate in a proper transverse-to-target orientation to detect passing targets, such as the brake rotor mounting bolts or magnets.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.13/719,137, filed on Dec. 18, 2012, now U.S. Pat. No. 9,244,090.

BACKGROUND INFORMATION

This invention relates to a compact, accurate and robust speed sensorfor motorcycles, all-terrain vehicles (ATVs), and the like.

Mechanisms for determining the speed of a motorcycle or ATV typicallyinvolve sensing the rotational speed of a wheel. The sensed informationis conducted to a meter for display, typically as linear velocity inunits such as miles per hour.

A preferable location for sensing the wheel speed is near the hub. Themain component of the sensor is fixed in place on the fork, for example,or on a stationary (that is, not rotating) bracket to which the brakecaliper is fastened. The main component of the sensor is thus positionedto detect the motion of one or more small, magnet “targets” that arecarried on the brake rotor and located to pass by the sensor as thewheel rotates.

Space for attaching the stationary component of the sensor is quitelimited, so a small sensor is necessary. It is also desirable toconfigure the sensor so that it remains intact, in place and functional,especially when used on an off-road type of motorcycle or ATV where thesensor may be subjected to potentially damaging elements such as shock,water, mud, brush, etc. In short, it is desirable to use a speed sensorthat is compact and robust.

One prior approach to sensing wheel rotation speed provides a hollow,metallic housing within which a reed switch is located. The housingincludes external threads and a cylindrical internal bore. The housingmay thus be in the form of a hollow bolt that can be threaded into acorresponding threaded aperture near the hub. The reed switch is anelectrical switch operated by an applied magnetic field. The switchconsists of a pair of contacts on ferrous metal reeds in an airtightglass envelope. The contacts are normally open, making no electricalcontact. The switch is actuated (closed) when a magnet that is carriedon the brake rotor is moved near the switch. Once the magnet moves past,the reed switch returns to its open state. Leads that extend from thereed switch are connected to wires that are inside of a cable thatextends from one end of the housing to a meter or computer on themotorcycle where the vehicle speed is calculated and displayed.

While the reed switch-type speed sensor just described has the attributeof compactness, it is insufficiently reliable, primarily because of therequirement for somewhat delicate moving parts: the thin metal reeds.

Another type of sensor, known as a Hall effect sensor, can be employedfor sensing wheel rotational speed. Hall effect sensors include a planarconductor, or Hall plate, along which a current is applied. Variationsin the magnetic flux through the plate produce a voltage across theplate that is directly related to the flux density. The magnetic fluxdensity variations can be provided by a magnet that moves past theplate. Alternatively, the Hall plate can be biased with a magnet so thatthe flux is varied by a ferrous target that moves past the plate throughthe magnetic field.

Some Hall effect sensors are available in integrated circuit (IC)packages. Such packages are typically planar in shape and have a flatface that must be oriented so that it is generally parallel to, and inclose proximity with, the path of the target as it moves across theplate. For convenience, this orientation of the Hall plate relative tothe target path will be here referred to as the “transverse-to-target”orientation.

While such Hall effect sensors are generally more reliable than reedswitches, they can be made more robust if they include additionalprotective circuitry for use of the sensor in a severe environment orwith an electrical system that is exposed to potentially damagingvoltage excursions.

The present invention is directed to a robust Hall effect sensor thatincludes such protective circuitry and is assembled within a compacthousing that can be attached to the wheel in the vicinity of the brakerotor to present the sensor Hall plate in a proper transverse-to-targetorientation to detect passing targets, such as the brake rotor mountingbolts.

Other advantages and features of the present invention will become clearupon study of the following portion of this specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a speed sensor assembly formed in accordancewith the present invention.

FIG. 2 is a vertical cross sectional view of the speed sensor assemblyof FIG. 1.

FIG. 3 is an enlarged perspective view of the speed sensor assemblyremoved from its housing.

FIG. 4 is a cross sectional view taken along lines 4-4 of FIG. 1.

FIG. 5 is an enlarged perspective view of the joined circuit board andflexible circuit member components of the speed sensor assembly.

FIG. 6 is an enlarged perspective view of the support component of thespeed sensor assembly.

FIG. 7 is an end view of a magnet used with the speed sensor assembly.

FIG. 8 is a circuit diagram of a preferred protection circuit that isemployed with the speed sensor assembly.

FIG. 9 is a side view of a wheel of a motorcycle with which the speedsensor assembly of present invention may be used.

DETAILED DESCRIPTION

FIG. 9 depicts a side view of a wheel 20 of a motorcycle with which thespeed sensor assembly 22 of present invention may be used. The wheel 20is carried on a central hub that extends between the spaced-apart legs24 of the motorcycle fork 26.

One fork leg 24 includes an attached rigid, metal extension 28, to whicha brake caliper mounting bracket 30 is fastened. The brake pads of thecaliper are applied to the disc or rotor 32 that is fastened to therotating hub by bolts 34.

The speed sensor assembly 22 is mounted to the caliper mounting bracket30 in an orientation that permits the Hall effect sensor component ofthe assembly to detect the presence of the heads of the ferrous bolts 34as the bolts pass adjacent to the sensor. The output of the sensorassembly is conducted via a cable 36 to a meter or computer for displayin units of velocity.

With reference to FIGS. 1-4, a preferred embodiment of a speed sensorassembly 22 includes a rigid, generally tubular housing 38 that may beformed of stainless steel, for example. At the outer end 40 of thehousing 38, the exterior surface is threaded. The exterior of themid-section 42 of the housing is hexagonal in cross section so that awrench or other driver can be applied for threading the outer end 40 ofthe housing into a correspondingly threaded aperture in the brakecaliper mounting bracket 30. In a preferred embodiment, the outer end 40of the housing 38 is in the form of a hollow 8 mm bolt.

The housing 38 has a generally cylindrical bore 46 extending through it.The bore 46 has a longitudinal axis 44. When threaded into the aperturein the caliper mounting bracket 30, the longitudinal axis 44 is parallelto the axis of rotation of the wheel 20 so that the path of the passingrotor bolts 34 is in a plane that is perpendicular to the longitudinalaxis 44 of the housing bore.

An annular, radially inwardly protruding shoulder 48 (FIG. 2) is formedin the bore 46 within the outer end 40 of the housing. One edge of adielectric seating ring 50 is abutted against the shoulder 48. A rigid,planar printed circuit board (PCB) 52 is seated on the other edge of theseating ring 50 and thus constrained from moving further inwardly of thehousing bore 46. An enlarged view of the PCB 52 appears in FIG. 5.

The rigid PCB 52 serves in part as a base for a back-biased, integratedcircuit (IC) Hall effect sensor 54, and for connecting the sensor'sthree leads 56 (supply, ground and output) to the corresponding supply,ground and output termini 58 of the three-conductor cable 36. The PCB 52also connects the sensor 54 with an associated severe-environment andelectronic system protection circuit 60 (hereafter “protection circuit”FIG. 8, discussed more below). The three conductor cable termini 58 areconnected to the PCB 52 at vias 68, and the three leads 56 from thesensor 54 are connected at adjacent vias 70 in the PCB 52.

The protection circuit 60 is provided on an elongated flexible printedcircuit (FPC) 62 that has one end joined to the PCB 52 along a flat sideedge region 64 of the PCB 52. At that edge region 64, the elongated FPC62 is bent and extends away from the PCB 52 in a direction generallyparallel to the longitudinal axis 44 of the housing bore 46. Theelectronic components 66 (FIG. 5) of the protection circuit 60 aremounted to the FPC 62 so that those components, as well as the elongatedFPC 62 are compactly housed within the assembly in a generally linearorientation, parallel to the longitudinal axis 44.

The Hall effect sensor IC 54 and an associated permanent magnet 72 aresecured within the housing bore 46 by a dielectric support 74 (see FIG.6). Specifically, the sensor 54 has a generally planar back surface thatis bonded to the flat surface that corresponds to the south pole of thepermanent magnet 72. That opposite surface of the magnet 72 rests on asupport surface 76 of a platform part 78 of the support 74.

As viewed from the end (that is, in the direction of the longitudinalaxis 44 of the housing bore 46) the support 74 has a shape thatgenerally conforms to that of the PCB 52, including a flat edge region80 that aligns with the flat edge region 64 of the PCB 52. The platformpart 78 of the support thus extends across the bore 46 of the housing,generally perpendicular to the longitudinal axis of the bore. Theunderside of the platform part (that is, the side facing the PCB 52)includes a peripheral edge that protrudes therefrom to define a supportrim 82 (FIGS. 4 and 6) that contacts the corresponding peripheral edgeof the PCB 52. That rim 82 thus defines a space between the platformpart 78 and PCB 52 to provide clearance for the soldered ends of theleads 56 and cable termini 58 that may protrude from the surface of thePCB 52. Preferably, the rim 82 also includes a radially inwardlyprotruding lip 86 (FIG. 2) that contacts the magnet-facing surface ofthe PCB 52 to enhance the stability of the support 74 against the PCB52.

On one edge of the platform part 78, the support 74 includes a riser 88(FIGS. 3 and 6) that extends away from that part along one side of themagnet 72. The riser 88 has formed in it three channels 90 within eachof which is received a lead 56 that extends from the Hall effect sensor54 to the PCB 52. The riser 88 is dielectric to insulate those leadsfrom each other and from the conductive wall of the housing bore 46.

With particular reference to FIGS. 3 and 4, the Hall effect sensor IC 54includes a planar outer surface 92 that covers the Hall plate of thesensor. The surface 92, hence the Hall plate, is arranged in thetransverse-to-target orientation relative to the passing targets (thatis, the heads of the rotor bolts 34) when the housing 38 is threadedinto the aperture in the caliper mounting bracket 30 as noted above.

One Hall effect sensor that is usable with the speed sensor assembly 22of the present invention is that manufactured by NV Melexis SA as modelnumber MLX90217. A suitable protection circuit 60 is shown in FIG. 8,where R1=5.6 kΩ, C1=10 nF, and C2=2.2 nF. D1 is a diode providingreverse polarity protection, and D2 is a Zener diode (24 volts) thatcombines with R1 to provide voltage protection.

The embodiment described above includes a permanent magnet 72 for backbiasing the Hall plate to thereby provide a magnetic field to enhancethe ability of the sensor to detect the relatively minor disturbance inthe field due to the passage of the ferrous targets. The magnet may be aneodymium magnet, grade N45 or N50, for example, and preferably has avery thin epoxy coating. FIG. 7 shows an end view of a preferred magnet72 as viewed from the end of the housing (that is, in the direction ofthe longitudinal axis 44 of the housing bore 46). The magnet 72 has agenerally circular cross section but for a small, trimmed side 94 of themagnet. This trimmed side 94 provides room for the support riser 88 toextend between the magnet 72 and the inner wall of the housing bore 46(FIG. 2). In this regard, the surface of the riser 88 that faces themagnet 72 is somewhat concave (FIG. 6), and the trimmed side 94 of themagnet 72 is contoured to be generally convex so that the magnet crosssectional shape occupies substantially the entire cross-sectional areaof the outer end of the housing bore 46. This provides the maximumamount of flux through the Hall plate for a given grade of magnet andinternal diameter of the housing bore.

As an alternative, the speed sensor assembly may be implemented withoutuse of a magnet for back-biasing the Hall plate. In such an embodiment,the back surface of the Hall effect sensor IC 54 would be secureddirectly to the support surface 76 of the support 74 (with the riser 88correspondingly shortened or eliminated), and one or more small magnets,such as shown at 96 in FIG. 9, are attached to the rotor for detectionby the sensor 54. It is noteworthy that such magnets may also be used astargets with the back-biased embodiment described above.

At the inner end 98 of the assembly housing 38, the wall thickness isreduced but for an annular ridge 100 around which tightly fits one endof a tapered rubber boot 102 through which the cable 36 extends from theother end of the boot (FIG. 2). The boot 102 provides strain relief forthe cable. To enhance the robustness of this cable-to-housingconnection, epoxy is injected into the void 104 between the boot 102 andcable 36 to bond those components together. Upon curing, the epoxyserves as enhanced strain relief between the cable and housing toprotect against damage or disconnection as a result of the elementsnoted above (shock, water, mud, brush, etc) that are common to theoff-road vehicles with which the speed sensor assembly of the presentinvention is intended to be used.

Preferably, the entire speed sensor assembly is encapsulated in epoxy.To this end, the flat side edge region 64 of the PCB 52, the flat edgeregion 80 of the support, as well as a pair of small notches 106 in theotherwise rounded side edge of the PCB 52 (see FIG. 5) provide passagesfor movement of the liquid epoxy through the housing bore for completeencapsulation. In this regard, the inventors have found that injectionof epoxy (as by a hypodermic-like needle) through the boot 102 forproviding the enhanced strain relief discussed above can also be usedfor flooding the assembly with the encapsulating epoxy in the directionof the inner end 98 to the outer end 40 of the housing. This approachhas the advantage (as compared to introducing epoxy inwardly from theouter end) of preventing the formation of air bubbles that would resultin an inferior encapsulation or potting of the assembly components.

While the foregoing description was made in the context of preferredembodiments, it is contemplated that modifications to those embodimentsmay be made without departure from the invention as claimed.

The invention claimed is:
 1. A method of assembling a speed sensor in ahousing that has cylindrical bore with a longitudinal axis, the methodcomprising the steps of: seating a planar circuit board in the bore toextend across the longitudinal axis; joining one end of an elongatedflexible circuit member to the circuit board so that the flexiblecircuit member extends therefrom in a direction generally parallel tothe longitudinal axis; providing a dielectric support for positioning inthe housing; and supporting a planar Hall effect sensor to extend acrossthe longitudinal axis of the bore so that leads of the sensor extendfrom the sensor and through spaced apart channels in the dielectricsupport for connection with the circuit board.
 2. The method of claim 1including the step of providing the sensor with a Hall plate at a frontsurface of the sensor and arranging the Hall plate to extendperpendicular to the longitudinal axis of the housing bore.
 3. Themethod of claim 1 including the step of supporting a magnet in the boreto abut a back surface of the sensor.
 4. The method of claim 3 includingthe step of shaping the magnet so that it occupies substantially theentire cross-sectional area of the bore.
 5. The method of claim 1including the step of seating the planar circuit board in a plane thatis generally perpendicular to the longitudinal axis of the housing, andshaping the circuit board to have a flat side edge at the junction ofthe flexible circuit member and the circuit board.
 6. The method ofclaim 1 including the step of mounting electrical components on theflexible circuit member to form a functional electrical circuit with theleads of the sensor.
 7. The method of claim 1 including the steps of:connecting to the circuit board the termini of a cable that extends froman inner end of the housing; and bonding to the cable a boot that fitsaround the inner end of the housing.
 8. The method of claim 7 includingthe steps of: injecting epoxy into the inner end of the housing forbonding the boot and cable, and directing the epoxy through the housingbore to an outer end of the housing, thereby encapsulating thecomponents of the assembled speed sensor.
 9. A method of assembling aspeed sensor in a housing that has cylindrical bore with a longitudinalaxis, the method comprising the steps of: seating a planar circuit boardin the bore to extend across the longitudinal axis; joining one end ofan elongated flexible circuit member to the circuit board so that theflexible circuit member extends therefrom in a direction generallyparallel to the longitudinal axis; providing a dielectric support forpositioning in the housing; supporting a planar Hall effect sensor toextend across the longitudinal axis of the bore so that leads of thesensor extend from the sensor and through the dielectric support forconnection with the circuit board; forming the housing to include anannular internal shoulder; and seating the circuit board on a dielectricseating ring that is located in the bore and abutting the internalshoulder.
 10. A method of assembling a speed, the method comprising thesteps of: providing a sensor housing that has a cylindrical bore with alongitudinal axis; seating a planar circuit board in the bore to extendacross the longitudinal axis; joining one end of an elongated flexiblecircuit member to the circuit board so that the flexible circuit memberextends therefrom in a direction generally parallel to the longitudinalaxis; supporting a planar Hall effect sensor to extend across thelongitudinal axis of the bore so that the leads of the sensor extendfrom the sensor and through a dielectric support for connection with thecircuit board; forming the housing to include an annular internalshoulder; and seating the circuit board on a dielectric seating ringthat is located in the bore and abutting the internal shoulder.
 11. Themethod of claim 10, including the step of providing the sensor with aHall plate at a front surface of the sensor and arranging the Hall plateto extend perpendicular to the longitudinal axis of the housing bore.12. The method of claim 10, including the step of supporting a magnet inthe bore to abut a back surface of the sensor.
 13. The method of claim12, including the step of shaping the magnet so that it occupiessubstantially the entire cross-sectional area of the bore.